Updated Mageia to 7.1, dropped old versions

src/mageia.ipxe

@@ -11,9 +11,7 @@ goto ${menu} ||
 :mageia
 set os Mageia
 menu Mageia - ${arch} - Image Sig Checks: [${img_sigs_enabled}]
-item 6 ${os} 6
-item 5 ${os} 5
-item 4 ${os} 4
+item 7.1 ${os} 7.1
 item cauldron ${os} cauldron
 choose version || goto mageia_exit
 goto mageia_boot